dogehouse: New Version Bug: Browsers without latest CSS standard have a broken UI

Description

So I use Firefox as my daily driver browser and whenever I go to check out the new design for DogeHouse, the UI always fails to load correctly. It is all stuck up against the left side of the screen, not in the center like it should be. Plus theres other things like the icons make the text thats supposed to be next to them go to the next line (or something like that). I even tried the new design in a version of Firefox on my computer that is basically a fresh install, no extensions, themes, etc. and that still didn’t work. Below I have attached screenshots of the new design in both the Brave browser and Firefox. The screenshots were both taken on the same monitor one after another.

Also, I have cloned the repo to my own computer which is up to date from origin at the time or writing this. This still did not work and the result was the same as on next.dogehouse.tv. This is confusing me as to why this is happening so if you have any ideas just let me know. If you need any more information please ask as I would be happy to provide any needed information or anything like that.

Reproduction

Open next.dogehouse.tv in a Gecko browser.

Expected Behavior

The UI should look the same on both Chromium and Gecko based browsers.

Screenshots

Brave Browser (Chromium Based)

Firefox Browser (Gecko Based)

Device

MacPro 3,1 (64 Bit) running 10.11.6

Additional Context

Firefox Version: 78.9.0esr (64-bit) Brave Version: 1.21.74 Screen Resolution: 1920x1080